This invention relates to engine analyzers in general and more particularly to an improved analyzer for analyzing the firing voltage curve of a spark plug in an internal combustion engine.
It is well recognized that internal combustion engines operated by spark plugs which are externally fired can suffer from various types of misfiring caused by spark plug defects. It is known that the type of defect can be recognized by an examaination of the firing voltage curves. Typically, the voltage curves are examined at the high voltage side of the ignition coil. Common causes of misfiring are those caused by lead coated or fouled spark plugs, by cracks in the plug insulator or by flash overs in the spark plug connection. In general then, two basic types of defects can be detected, one caused by fouling and the other caused by flash over either because of a crack in the insulation or some other reason. A determination of these misfiring and their type can be accomplished by wave-shape analysis using an oscilloscope. Typical of such instruments is that described in German Auslegschrift 1,288,853. However, the use of this type apparatus presupposes heavy practical experience in order that a correct diagnosis be made from the path of the curve. Furthermore, interpretation of the oscilloscope pattern is made more difficult if misfirings occur only intermittently. This is particularly true if for multi-cylinder engines where the intermittent error curve must be selected from among a plurality of proper firing curves, each of which differs from one another.
A type of automatic detection equipment is disclosed in German Augslegsschrift 2,040,913. This device provides for automatic detection of the wave-shape of the firing voltages in a multi-cylinder external combustion engine without the need for an oscilloscope. In the device described therein, a plurality of measuring channels are provided which scan the firing voltage curves in consecutive time periods under control of a control unit with time slots assigned to the individual channel for storing the scanned values. A corrolator is then used to insure that the firing voltage curves are assigned to corresponding cylinders of the engine.
Clearly, it can be seen that these devices of the prior art suffer from serious disadvantages; the oscilloscope requires well trained operators and has the difficulty of detecting intermittent faults and the above described automatic type device is quite complex. Thus, there is a need for an improved device of this nature which is simple to operate and not prohibitively expensive to build.